Purification of tar acid-bearing oils



Patented Sept. 15, 1931 vireo STATES PATENT OFFICE STEPHEN P. BURKE, OFNEW YORK, N. Y., ASSIGNOB TO OOMBUSTION-UTILITIES CORPORATION, OF NEWYORK, N. Y., A CORPORATION'OF MAINE PURIFICATION OF TAR ACID-BEARINGOILS No Drawing.

7 The present invention relates to the purification of tar acid-bearingoils, and more particularly to a process for eliminating colorproducingcompounds from tar acid-bearing 5 oils containing them. I I

Some tar acid-bearing oils (such as low temperature tars, blastfurnacetars, vertical retort tars, shale oils and other liquid'condensates resulting from the distillation of bituminous materialunder carbonizing conditions mild enoughto preserve the liquidby-products in a substantially primary and undecomposed form) containcertain impurities which render them unsatisfactory or make themundesirable for certain uses. One form in which these impuritiesmanifest themselves is in the production of colored compounds when suchoils are "used for the manufacture of disinfectants, animal dips,saponified cresol or tar acid'solutions and related products; Afterexhaustive and thorough investigation of the chemical compositions andproperties of these colored compounds their origin has been traced tocertain strongly reducing ortho-dihydrictar acids, similar to but notincluding catechol. Thus one of these bodies has been isolated andidentified as a new homologue of catechol comprising 3, 4- or 3,G-dimethyl catechol.

The primary object of the present invention is to provide a process forremoving color producing compounds of the type referred to from taracid-bearing oils containing them. Heretofore in preparing and refiningtar acid-bearing oils of the class described for use in the manufactureof disinfectants, animal dipsand similar products, the oils have beensubjected to washing treatments with aqueous sodium carbonate solution.This treatment, however, failsto give even approximately completeremoval of the color forming matter except with oils which containunusually small amounts of such colorproducing bodies. In treating othertar acid-bearing oils, washing with dilute caustic soda solution hasbeen employed, but this treatment involves a very considerable loss ofthe desirable tar acids of-high germicidal.

value, which areextracted together with the color-forming materials. bythe caustic soda Application filed September 22, 1926. Serial No.137,174.

treatment. Another method has been recent lyproposed for removing thesecolor producing compounds from coal tar distillates and the like, whichcomprises washing theoils with aqueous solutions of weakly alkalinebuffer agents such as calcium hydroxide and ammonium hydroxide. Whilethis latter method of treatingthe'oils has proved to be much moresatisfactory than methods now in use in the trade,- it has been foundthat the action of the alkaline buffer agents is often incomplete in thecase of taracid-bearing oils containing appreciably large quantities ofcolor-producing matter. Fractionation of the oilswith rejection of theportion boiling above-230 C. has alsobeen advocated, but since thisexcludes the larger'portion of the oil, including most of the highboiling tar acids which are the most valuable germicides present in theoils, the method is not commercially feasible.

Another objectof the present invention is to provide a process by whichthe color-producing bodies present in such tar acid-bearing oils can becheaply and completely extracted without also removing valuable taracids.

With these and other objects and features in view the invention consistsin the process for purifying tar acid-containing oils hereinafterdescribed and particularly defined in the claims. a

Essentially the. process for purifying tar acid-bearing oils forming thesubject of the present invention, in its preferred form, consists inprecipitating the color-producing bodies from the oil by means of awater-solublenon-acidic salt of aheavy metal, parblack, fullers earth,activatedcarbon or the tar acids from a tar acid-bearing oil. Nofavorable catalysis of secondary reactions with the color-producingcompounds appears to takeoplace, and practically none of the desirableand valuable monohydroxy tar acids of high germicidal value areprecipitated from theoil.

The following procedure isset forth as an example of a satisfactorymethod of treating tar acid-bearingoilshaving a relatively bidowing-tothe presence of gelatinous lead salts of color-producingimpurities original- 1y present in the oil, was mixed with 1% of itsweight of a filter-aid (for example bone like) and filtered withsuction. The resulting oil filtrate was clear, and a disinfectantprepared from it by means of. rosin soap gave an emuls1on with waterwhich was practically free of red color. The oil may be distilled eitherbefore or after treatment if desired, although such distillation is notnecessary for the'removal of the color-producing bodies. Without the useof some filter aid such as bone black, fullers earth or the like,experiments have shown that it is extremely difficult to get a complete,separation of the insoluble lead salts of the color-producing-bodiesfrom the oil in which they are suspended. Filtration or centrifuging ofthe oil has been tried, butin many cases the oil obtained by either ofthese treatments is not entirely freed ofv the insoluble salts of thecolor-producing bodies. It has been found desirable to heat the oilduring the period of agitation with thetreating agent, forthe reasonthat since the reaction leading to'the formation of insoluble metalsalts takes place in the aqueous phase,the heat increases the solubilityof thecolor-forming material in the aqueous phaseand thereby hastens thecompletion of the reaction and insures the completeness of interactionbetween the reagent and the color-producing impurities. Once formed, theinsoluble metal salts leave the aqueous phase and pass into the oil,where'they remain in suspension. If an excess of the precipitating agentis present in the aqueous solution, the latter may be drawn off and usedagain for treating another batch of oil, and this process reagentremains in the aqueous solution.

It is not intended by the above description to limit the scope of thepresent invention to the treatment of oils containing definitecompounds, nor to the use of definite proportions of the precipitatingagent, nor to the employment of particular temperatures or particulartime limitations of agitation, nor to the use of any particular metalsalt as a precipitating agent or particular methods of separating theoil and insoluble material@ Any metal salt which gives an insolublecompound on interaction with orthodihydric tar acids of the classreferred to may be employed. The process is applicable not only to thetreatment of the tars themselves, but also to the treatment of a taracid fraction alone (unadmixed with hydrocarbon oil), The volume 'of theprecipitating agent used is preferably limited to a. slight excess abovethat required for removing the color-producing impurities.

By employing the process forming the subject matter of the presentinvention for the purification of tar acid-bearing oil, disinfectantemulsions can be prepared from a soap base blend of the oil which willnot turn pink, and the purification of the oil can be completed atrelatively small expense without materially lowering the value of thedisinfectants and the germicidal agents prepared therefrom.

' The term tar acid-bearing oil is used in the description and claims toinclude all tar acid containing oils or liquid condensates obtained inthe distillation of coal or oil shale. The tar acid content of most ofsuch oils, and particularly those obtained by the low temperaturedistillation of coal, often consists almost entirely of compounds,which, while they resemble the, phenols or tar acids of coke oven tar insome of their properties, do not come within the generally accepteddefinition of a phenol, but are rather hydroxyl derivatives of cyclichydrocarbons which are nonaromatic in character, having hydrogen andalkvl side chains attached to the aromatic nucleus.

The preferred form of the invention having been thus described, what isclaimed as new 1s: I

1; The method of removing color-produc- Iing compounds from an oilcontaining mono- 7 producing bodies thereby precipitated from peatedaslong as suiiicientprecipitating the residual purified oil. 3. The methodof removing color-producmg compounds, including ortho-dihydric taracids, from an oil containing the same together with other tar acidswithout substantial removal of the latter from the oil which comprisesagitating a mixture of the oil and a non-acidic salt ofa metal whichforms insoluble compounds with ortho-dihydric tar acids, andsubsequently separating the purified oil and the, insoluble compoundsthus formed.

4. The method of removing color-producing compounds, includingortho-dihydric tar acids, from an oil containing the same together withother tar acids without substantial removal of the latter from the oilwhich comprises agitating a mixture of the oil and an aqueous solutionof a non-acidic salt of a metal which forms insoluble compounds withortho-dihydric tar acids, and separating the insoluble compounds thusformed from the residual oil.

5. The method of removing color-producing compounds from an oilcontaining monohvdric tar acids while conserving the content of thelatter, which comprises agitating the oil for about thirtv minutes at atemperature of about C. with about an equal volume of a 10% aqueoussolution of normal lead acetate, separating the aqueous layer from thetreated oil. mixing with the latter a small percentage of a filter aidmaterial, and filtering to separate the insoluble metal saltprecipitates of the color-producing bodies from the oil filtrate.

6. The method of removing color-producing compounds from an oilcontaining monohvdric tar acids while conserving the content of thelatter, which comprises agitating the oils with an aqueous solution ofnormal lead acetate.

7. The method of removing color-producing compounds from an oilcontaining monohvdric tar acids while conserving the content of thelatter, which comprises agitating the oil with an aqueous solution of anon-acidic salt of a heavy metal, separating the aqueous solution ofexcess treating agent from the treated oil, and employing the solutionthus separated in purifying another batch of oils containing tar acid.

8. The method of removing color-producing compounds from an oilcontaining monohvdric tar acids while conserving the content of thelatter, which comprises agitating the oils with an aqueous solution of anon-acidic salt of a heavy metal, separating the aqueous layer from thetreated oil, mixing with the oil layer a small percentage of a filteraid and filtering to separate the insoluble metal salt precipitates fromthe oil filtrate.

In testimony whereof I aflix mv signature.

STEPHEN P. BURKE.

